A method of preparing 1, 1-Dialkoxycycloalkanes

Abstract: 1,1-Dialkoxycycloalkanes of the structure (II) wherein R 1 and R 2 are different or the same alkyl moieties and can be a saturated, unsaturated, branched, unbranched or cyclic alkyl moiety of 1-3 carbon atoms and n is an integer from 4 to 9, are prepared by first anhydrously reacting hydrogen cyanide or a hydrogen cyanide derivative with a secondary alkanol and hydrogen chloride in the presence of an inert organic solvent. Upon the formation of the resulting imino ether hydrochloride more secondary alkanol and a cycloalkanone having 5 to 10 carbon atoms are added to form the 1,1-dialkoxycycloalkanes (II).

Description: The present invention relates to a "one-pot" preparation of 1,1-dialkoxycycloalkanes. The 1,1-dialkoxycycloalkanes are compounds of the structure (II) wherein R 1 and R 2 correspond to R 1 and R 2 of structure (I), and n is an integer from 4 to 9. The 1,1-dialkoxycycloalkanes defined by structure (II) can be used as protective or blocking structures for the alcohols corresponding to the alkoxy groups. The alcohols can be regenerated under acidic conditions. The compounds defined by structure (II) are also useful intermediates in the manufacture of pharmaceutical, photographic or agricultural products. In the process of the invention, compounds of the structure (II) are prepared by first preparing an imino ether hydrochloride by reacting hydrogen cyanide with a secondary alkanol and hydrogen chloride in the presence of an inert organic solvent, followed by the addition of a cycloalkanone and secondary alkanol to the reaction mixture containing the imino ether hydrochloride. D P Roelofsen and H van Bekkum describe in Synthesis 8 , 419-420 (1972) the preparation of dialkoxycycloalkanes by reacting a cycloalkanone with a secondary alcohol in the presence of an acidic catalyst and a molecular sieve. Methoden der organischen Cherine, Band V1/3 (1965) states that dialkylacetals may be prepared by the reaction of a ketone with excess alkanol and an imino ether hydrochloride. It is also known that 1,1-dialkoxycycloalkanes can be prepared by reacting cycloalkanones with alcohols in the presence of an acid catalyst. The present invention provides a novel method: cycloalkanone and secondary alkanol are added to a reaction mixture in which an imino ether hydrochloride has been produced. Summary of the Invention The process of the invention is directed to the preparation of 1,1-dialkoxycycloalkanes of the structure (II) wherein R 1 and R 2 are different or the same alkyl moiety having from 1 to 3 carbon atoms and n is an integer from 4 to 9. Compounds of the structure (II) are prepared by first anhydrously reacting hydrogen cyanide, or a derivative of hydrogen cyanide, with a secondary alkanol and hydrogen chloride in the presence of an inert organic solvent. In the reaction mixture, an imino ether hydrochloride of the structure (III) forms wherein R 1 and R 2 correspond to R 1 and R 2 of structure (II). Compounds of the structure (II) are formed by adding to the reaction mixture containing the imino ether of the structure (III) more secondary alkanol and a cycloalkanone having 5 to 10 carbon atoms. Detailed Description of the Invention The present invention relates to the preparation of 1,1-dialkoxycycloalkanes of the structure (II) (described above, hereinafter "dialkoxycycloalkanes II"). The initial step in the preparation of the dialkoxycycloalkanes II is the preparation of a reaction mixture containing an imino ether hydrochloride of the structure (III) (described above, hereinafter "imino ether III"). The imino ether III is prepared by anhydrously reacting hydrogen cyanide, or a derivative of hydrogen cyanide, with hydrogen chloride and a secondary alkanol of the structure (IV) wherein R 1 and R 2 correspond to R 1 and R 2 of the dialkylcycloalkanes II. As used herein, the term "alkyl moiety" or "alkyl group" used in reference to R 1 and R 2 means any alkyl group of 1-3 carbon atoms and includes, without limitation, saturated, unsaturated, branched, unbranched and cyclic alkyl groups. Examples of secondary alkanols of the structure (IV) are 2-propanol, 2-butanol, 3-methyl-2-pentanol, 2-pentanol, 3-pentanol and 3-heptanol. In the initial reaction, hydrogen cyanide can be replaced with a derivative of hydrogen cyanide. Hydrogen cyanide, however, is preferred. Useful derivatives include compounds of the structure RCN, wherein R is an alkyl group of 1-2 carbon atoms. Useful derivatives include, for example, acetonitrile. Derivatives which include alkyl groups of more than two carbon atoms can slow the reaction appreciably. The reaction must be carried out under anhydrous conditions. This requirement will be met if the overall content of water in the reaction mixture is lower than the preferable limit of about 1,000 ppm. The reaction mixture should remain anhydrous throughout the preparation of the dialkoxycycloalkanes II. In the preparation of the imino ether III, it is preferable to add the reactants approximately simultaneously to the reaction vessel. While it is sufficient to add approximately equimolar concentrations of the reactants to the reaction vessel a slight excess of the secondary alkanol and hydrogen chloride is preferred. The preferable molar ratio of hydrogen cyanide, or hydrogen cyanide derivative, to secondary alkanol to hydrogen chloride is 1:1.05:1.10. The addition of the reactants can be done in any practical manner, but a continuous addition over a 10 to 12 hour period at a temperature within the range of about 0°C to 30°C is preferred. Once the addition is completed, it is preferable to stir the reaction mixture for about 6 to 8 hours at a temperature within the range of about 0°C to 30°C. Following this process, it is possible to obtain an almost quantitative yield of the imino ether III. Prior to the addition of the reactants, the reaction vessel should be charged with an organic solvent. A preferred solvent is any solvent which is essentially anhydrous, does not participate in the reaction and does not dissolve ammonium chloride formed as a by-product. Appropriate solvents include, but are not limited to, n-hexane, cyclohexane, heptane, carbon tetrachloride, decalin, petroleum ether, 2,2,4-trimethylpentane, benzene, ethylbenzene, mesitylene, toluene, and xylene, or mixtures thereof. The amount of solvent is preferably at least equal to the molar amount of hydrogen cyanide to be added and, more preferably, more than twice the total molar amount of hydrogen cyanide and secondary alkanol to be added. If the amount of solvent is too low, the slurry which develops during the formation of the imino ether III will not stir effectively. As stated, it is preferred to carry out the synthesis of the imino ether III at a temperature within the range of about 0°C to 30°C. Above 30°C, the imino ether III should form but it may subsequently decompose, thereby decreasing the ultimate yield of the dialkoxycycloalkane II prepared thereafter. Below 0°C, the imino ether III can form but the reaction time may become prohibitively long in duration. A lengthy reaction time would be an obvious detriment in industrial applications. The optimum temperature depends in part-on the type of solvent used. With a nonpolar solvent, such as carbon tetrachloride, a temperature within the range of about 10°C to 20°C is preferred. With a polar solvent, such as chloroform, a temperature within the range of about 10°C to 30°C is preferred. From the imino ether III, the dialkoxycycloalkane II can be prepared. Separation or purification of the imino ether III, however, is not necessary. Concentration of the reaction mixture under reduced pressure can be done if desired. The dialkoxycycloalkane II is prepared from the reaction mixture containing the imino ether III. To the reaction mixture, a cycloalkanone and more secondary alkanol are added. Prior to the addition of each reactant, however, the concentration of hydrogen chloride in the reaction mixture should be adjusted to within the range of 1% to 5% by weight of the total mixture. The preferred concentration is about 3%. The reaction mixture can be so adjusted by the addition of a base which should be any basic substance which does not give rise to water. Such basic substances include metallic potassium, metallic sodium, potassium alcoholate, sodium alcoholate, ammonia, methylamine, trimethylamine, ethylenediamine, and diethylenediamine. The preferred base is ammonia gas. If an alcoholate is used, it should be based on the same alcohol as the secondary alcohol employed in the reaction. If the concentration of hydrogen chloride exceeds 5%, the ultimate yield of dialkoxycycloalkane II can decrease. If the concentration of hydrogen chloride falls below 1%, the reaction time can become too lengthy. After the concentration of hydrogen chloride has been adjusted, secondary alkanol is added in an amount at least twice the molar amount of the imino ether III (assuming a quantitative yield). That is, the secondary alkanol is added in an amount at least twice the molar amount of hydrogen cyanide, or hydrogen cyanide derivative, initially added. More preferably, the amount of secondary alkanol added should be between 2 and 3 times the molar amount of imino ether III. After or with the addition of the secondary alkanol, a cycloalkanone having a ring structure comprising 5 to 10 carbon atoms is added to the reaction mixture. It is preferred to add the cycloalkanone after the addition of the secondary alkanol. The amount of cycloalkanone to be added is at least equal to the molar amount of imino ether III (assuming a quantitative yield). That is, the amount of cycloalkanone to be added is at least equal to the molar amount of hydrogen cyanide, or derivative thereof, initially added. The reaction is preferably carried out at a temperature within the range of 20°C to 50°C and, more preferably, at about 40°C. Above 50°C, the dialkoxycycloalkanes II may decompose to an olefinic ether. Below 20°C, the reaction may proceed too slowly. The reaction is preferably carried out, within the preferred temperature range, at a pH of 2-3 for a period of 10 to 24 hours and, more preferably, for about 18 hours. It is preferred to carry out the preparation of the dialkoxycycloalkanes II under vacuum to minimize the potential loss of hydrogen chloride and hydrogen cyanide from the system. After the preparation of the dialkoxycycloalkane II, the reaction product can be separated from the reaction mixture, as is further explained below. The reaction mixture should first be cooled to a temperature of about 25°C, and preferably to below 10°C, and filtered to remove the ammonium chloride which forms as a by-product. To the filtrate, a base should be added to raise the pH to a level greater than about 7 and preferably within the range of about 8 to 10. Basic substances which can be used to raise the pH include alkali metals, such as potassium and sodium, alcoholates, methylamine, ethylenediamine, diethylenediamine and aqueous caustic solution. If aqueous caustic solution is used, the organic phase should be separated prior to separation of the dialkoxycycloalkane II to minimize the potential decomposition of either product. The dialkoxycycloalkane II can then be obtained by distillation. When the secondary alkanol is present in the reaction mixture, the dialkoxycycloalkane II remains stable even in the presence of ammonium chloride. If the secondary alkanol is a low-boiling alcohol, and evaporates during the filtration of the ammonium chloride, the dialkoxycycloalkane II can become unstable. Thus, it is preferable to carry out the filtration under conditions which would inhibit the removal of the secondary alkanol. For example, carrying out the filtration at a relatively cool temperature should be effective. The following examples further illustrate the process of the invention, examples 1, 3 and 4 not leading to ultimate products according to the invention but describing the preparation of intermediate used in the remaining examples which lead to products according to the invention. Example 1 Preparation of 1,1,1-Triisopropylorthoformate A one liter, 5 necked flask was equipped with an overhead stirrer, thermometer, addition funnel, gas inlet tube, and vacuum outlet through a manostat. Anhydrous toluene was charged into the flask and the system was evacuated with a water aspirator to about 20-22 inches Hg (68-75 kPa). The entire reaction was carried out under vacuum in order to minimize the loss of hydrogen chloride and hydrogen cyanide from the system. The addition funnel was connected to a mixture of hydrogen cyanide (27.0 g) and 2-propanol (63.0 g). This mixture was named the "mixed feed". The toluene in the flask was cooled to about 10-15°C, and hydrogen chloride was bubbled through at a rate so as to maintain the system under vacuum. When about 10% of the hydrogen chloride was added, addition of the mixed feed began. The remainder of the hydrogen chloride and mixed feed was added, and reaction mixture stirred, at a rate sufficient to maintain the temperature of the mixture within the range of about 10°C to 20°C. The addition was done over a four hour period. The imino ether hydrochloride salt crystallized out of the reaction mixture. The temperature was maintained below 20°C to prevent decomposition of the imino ether hydrochloride. After the addition, the reaction was stirred for about 8 hours at 20-25°C. Gaseous ammonia was then added to adjust the pH to 4-5 and neutralize the excess hydrogen chloride, during which time the temperature was maintained around 20°C. 2-propanol (150.0 g) was then added in one lot. The temperature of the mixture was raised and maintained at 30-35°C for about 10 hours. Ammonium chloride was filtered off, and the organic phase was washed with a 25% aqueous caustic solution (50 ml). The organic phase was separated from the aqueous phase and distilled under reduced pressure (10 mm Hg; 1.3 kPa). 135 g (70% yield) of 1,1,1-triisopropylorthoformate was obtained, with a purity of at least 98% as determined by gas chromatographic assay. Example 2 Preparation of 1,1-(Dipropan-2'-oxy)cyclohexane A one liter, 5 necked flask, equipped as in Example 1, was charged with toluene, hydrogen cyanide, hydrogen chloride and isopropyl alcohol in the manner and amounts disclosed in Example 1. A reaction mixture containing an imino ether hydrochloride salt was obtained in accord with Example 1. Gaseous ammonia was used to neutralize excess hydrogen chloride in the mixture to a level of about 3-5%. During the neutralization, the temperature was maintained at 15-20°C. The mixture was then charged with 2.5 equivalent of 2-propanol relative to the imino ether hydrochloride and 1 equivalent of cyclohexanone. The reactants were added simultaneously. The temperature was allowed to reach about 23°C before external heating was applied to maintain the temperature at about 40°C for about 24 hours. The ammonium chloride was filtered off and the organic phase was washed with a 25% caustic solution (50 ml). The organic phase was separated from the aqueous phase and 1,1-(dipropan-2'-oxy)cyclohexane was isolated by distillation. 75 g (50% yield) was obtained with a purity of at least 98% as determined by gas chromatographic assay. Example 3 Preparation of Tri(2-pentyl)orthoformate A one liter, 5-necked flask is equipped as in Example 1. Anhydrous toluene (2 mole equivalents) is charged into the flask and the system is evacuated with a water aspirator to about 20-22 inches Hg (68-75 kPa). The entire reaction is carried out under vacuum. The addition funnel is charged with a mixture of hydrogen cyanide (27.0 g) and 2-pentanol (92.4 g). This mixture is the "mixed feed". The toluene in the flask is stirred and cooled to about 10-15°C, and hydrogen chloride is bubbled through at a rate so as to maintain the system under vacuum. When about 10% of the hydrogen chloride is added, addition of the mixed feed is commenced. The remainder of the hydrogen chloride and mixed feed is added, and the reaction mixture stirred, at a rate sufficient to maintain the temperature of the reaction mixture within 10-20° C. The addition is done over a four hour period. The imino ether hydrochloride salt crystallizes out of the reaction mixture. The temperature is maintained below 20°C to prevent decomposition of the imino ether hydrochloride. After the addition, the reaction is stirred for about 20 hours at 20-25°C. The reaction mixture is cooled to 15°C and gaseous ammonia is added to adjust the pH to 4-5 and neutralize the excess hydrogen chloride. 2-Pentanol (220.0 g) is then added in one lot. The temperature of the reaction mixture is raised and maintained at 40-50°C for about 12 hours. Ammonium chloride is filtered off, and the organic phase is washed with a 25% aqueous caustic solution (50ml). The organic phase is separated from the aqueous phase and distilled under reduced pressure (5 mm Hg; 0.7 kPa) to yield tri(2-pentyl)orthoformate. Example 4 Preparation of Tri(3-pentyl)orthoformate A one liter, 5-necked flask is equipped as in Example 3. Anhydrous toluene (2 mole equivalents) is charged into the flask and the system is evacuated with a water aspirator to about 20-22 inches Hg (68-75 kPa). The entire reaction is carried out under vacuum. The addition funnel is charged with a mixture of hydrogen cyanide (27.0 g) and 3-pentanol (92.4 g). This mixture is the "mixed feed". The toluene in the flask is stirred and cooled to about 10-15°C, and hydrogen chloride is bubbled through at a rate so as to maintain the system under vacuum. When about 10% of the hydrogen chloride is added, addition of the mixed feed is commenced. The remainder of the hydrogen chloride and mixed feed is added, and the reaction mixture stirred, at a rate sufficient to maintain the temperature of the reaction mixture within 10-20°C. The addition is done over a four hour period. The imino ether hydrochloride salt crystallizes out of the reaction mixture. The temperature is maintained below 20°C to prevent decomposition of the imino ether hydrochloride. After the addition, the reaction is stirred for about 20 hours at 20-25°C. The reaction mixture is cooled to 15°C and gaseous ammonia is added to adjust the pH to 4-5 and neutralize the excess hydrogen chloride. 3-Pentanol (220.0 g) is then added in one lot. The temperature of the reaction mixture is raised and maintained at 50-60°C for about 12 hours. Ammonium chloride is filtered off, and the organic phase is washed with a 25% aqueous caustic solution (50ml). The organic phase is separated from the aqueous phase and distilled under reduced pressure (5 mm Hg; 0.7 kPa) to yield tri(3-pentyl)orthoformate. Example 5 Preparation of 1,1-(Dipentan-2'-oxy)cyclodecane A one liter, 5-necked flask, equipped as in Example 3, is charged with toluene, hydrogen chloride, hydrogen cyanide and 2-pentanol in the manner and amounts disclosed in Example 3. A reaction mixture containing an imino ether hydrochloride salt is obtained in accord with Example 3. Gaseous ammonia is used to neutralize the excess hydrogen chloride in the mixture to a level of about 3-5%. During the neutralization, the temperature is maintained at 15-20°C. The mixture is then charged with 2.5 equivalents of 2-pentanol relative to the imino ether hydrochloride and 1 equivalent of cyclodecanone. The reactants are added simultaneously. The temperature is allowed to reach about 25°C before external heating is applied to maintain the temperature at about 40°C for about 24 hours. The ammonium chloride is filtered off and the organic phase is washed with a 25% caustic solution (50ml). The organic phase is separated from the aqueous phase and 1,1-(dipentan-2'-oxy)cyclodecane is isolated by distillation under reduced pressure. Example 6 Preparation of 1,1-(Dipentan-3'-oxy)cyclooctane A one liter, 5-necked flask, equipped as in Example 3, is charged with toluene, hydrogen chloride, hydrogen cyanide and 3-pentanol in the manner and amounts disclosed in Example 4. A reaction mixture containing an imino ether hydrochloride salt is obtained in accord with Example 4. Gaseous ammonia is used to neutralize the excess hydrogen chloride in the mixture to a level of about 3-5%. During the neutralization, the temperature is maintained at 15-20°C. The mixture is then charged with 2.5 equivalents of 3-pentanol relative to the imino ether hydrochloride and 1 equivalent of cyclooctanone. The reactants are added simultaneously. The temperature is allowed to reach about 25°C before external heating is applied to maintain the temperature at about 40°C for about 24 hours. The ammonium chloride is filtered off and the organic phase is washed with a 25% caustic solution (50ml). The organic phase is separated from the aqueous phase and 1,1-(dipentan-3'-oxy)cyclooctane is isolated by distillation under reduced pressure.

Claims: A method of preparing a dialkoxycycloalkane of the structure (II) wherein R 1 and R 2 are different or the same alkyl moiety, said alkyl moiety having from 1 to 3 carbon atoms and n is an integer of from 4 to 9, the method comprising making an imino ether hydrochloride in an organic solvent by anhydrously reacting in the solvent hydrogen cyanide or hydrogen cyanide derivative, hydrogen chloride and a secondary alkanol of the structure (IV) wherein R 1 and R 2 correspond to R 1 and R 2 of structure (II), and anhydrously reacting with the imino ether hydrochloride additional secondary alkanol of the structure (IV) and a cycloalkanone having from 5 to 10 carbon atoms in the ring structure of the cycloalkanone, by adding the additional secondary alkanol in a molar amount equal to at least twice the molar amount of hydrogen cyanide or hydrogen cyanide derivative used to make the imino ether hydrochloride, and adding the cycloalkanone in a molar amount equal to at least the molar amount of hydrogen cyanide or hydrogen cyanide derivative used to make the imino ether hydrochloride. A method as claimed in claim 1, wherein approximately equimolar quantities of the hydrogen cyanide or hydrogen cyanide derivative, the hydrogen chloride and the secondary alkanol are added to the solvent. A method as claimed in claim 1 or claim 2, wherein, while reacting the hydrogen cyanide or hydrogen cyanide derivative, the hydrogen chloride and the secondary alkanol, the temperature is maintained within the range of 0°C to 30°C. A method according to any preceding claim, wherein, in the preparation of the imino ether hydrochloride, the hydrogen cyanide or hydrogen cyanide derivative, hydrogen chloride and secondary alkanol are reacted in a molar ratio of hydrogen cyanide or hydrogen cyanide derivative to secondary alkanol to hydrogen chloride of 1:1.05:1.10. A method according to any preceding claim, wherein the organic solvent is inert in the reaction mixture and does not dissolve ammonium chloride. A method according to any preceding claim, wherein the organic solvent comprises n-hexane, cyclohexane, carbon tetrachloride, decalin, petroleum ether, 2,2,4-trimethylpentane, benzene, ethylbenzene, mesitylene, toluene, xylene or chloroform. A method according to claim 6, wherein the organic solvent comprises toluene. A method according to any preceding claim, wherein the hydrogen cyanide or hydrogen cyanide derivative, hydrogen chloride and secondary alkanol of the structure (IV), are reacted in a polar solvent at a temperature within the range of 10°C to 30°C, or in a non-polar solvent at a temperature within the range of 10°C to 20°C, to form the imino ether hydrochloride. A method according to any preceding claim, wherein the additional secondary alkanol is added in a molar amount between 2 and 3 times the molar amount of hydrogen cyanide or hydrogen cyanide derivative used to make the imino ether hydrochloride. A method according to any preceding claim, wherein, while reacting the additional secondary alkanol and cycloalkanone with the imino ether hydrochloride, the solvent is maintained at a temperature of 20°C to 50°C. A method according to any preceding claim and further comprising, prior to reacting the imino ether hydrochloride with the additional secondary alkanol and the cycloalkanone, adjusting the hydrogen chloride concentration in the solvent to 1% to 5% by weight of the total mixture. A method according to claim 11, wherein the hydrogen chloride concentration is adjusted to 3% by weight of the total mixture. A method according to any preceding claim, wherein the cycloalkanone is added after the additional secondary alkanol has been added to the solvent containing the imino ether hydrochloride. A method according to any preceding claim, wherein the reaction of the imino ether hydrochloride, additional secondary alkanol and cycloalkanone is carried out at a pH of 2 to 3. A method according to any preceding claim, wherein the secondary alkanol is selected from the group consisting of 2-propanol, 2-butanol, 3-methyl-2-pentanol, 2-pentanol, 3-pentanol and 3-heptanol.

Inventors: BITLER GEORGE W, COLVIN DAVID, JOHN THOMAS V, SUBRAMANIAM CHITOOR S, BITLER, GEORGE W., COLVIN, DAVID, JOHN, THOMAS V., SUBRAMANIAM, CHITOOR S.
Applicants: CREANOVA INC, CREANOVA, INC.
Application year: 1994
Main classification: C07C41
IPC codes: C07C41, C07C257